The present invention concerns processes and apparatus for determining coil connections' resistance and coils' electric resistance by means of testing machines used in production lines for manufacturing dynamoelectric core components and their related windings, for example in the manufacturing of armatures of electric motors.
A coil connection is typically made for each coil to a commutator bar, or other terminal means for passage of electric current between each coil and an external supply. The coil connection is normally accomplished by positioning and fusing the lead conductor of the coil to or terminal, which has the form of a hook (“tang”) or other suitable configuration.
Fusing machines for permanently anchoring a lead conductor to a commutator bar have been described in EP 0419, 849 A1. Machines for forming coils of windings of cores of dynamoelectric machines have been described in EP 484,766 A2.
The quality of the manufactured connection is verified by testing devices, which measure the electrical resistance of the connections to the commutator bar, or to any other type of terminal means. This electrical resistance is indicative of the quality of the connection made, i.e. whether the lead has been anchored with the required electrical and mechanical properties.
In addition to measuring the electrical resistance of the coil connections, the electric resistance of the coils is also verified. The electric resistance of a coil is indicative of the number of turns that have been wound, and whether the conductor has been excessively elongated or insufficiently tightened by the tension applied during winding.
A process for determining the electric resistance of coil connections of a winding of a dynamoelectric machine having the characteristics of the preamble of method claim 1, and an apparatus according to the preamble of claim 8 have been described in U.S. Pat. No. 4,651,086 and EP 695,946A2.
The testing device of the foregoing prior art circulates electric current each time only through certain coils of the winding that have connections that need to be determined. In addition, a feedback regulating loop circuit is used to eliminate the current circulating in a remaining series of coils, whilst maintaining the opposite leads of this remaining series of coils substantially at the same voltage. In this way, the measurement and knowledge of the voltage and current of the coils where the current is circulating makes it possible to determine their electric resistance and the electric resistance of their connections.
The drawback of this prior art is that the current circulating through the coils that are being verified is influenced and in part derives from the above mentioned feedback regulating loop circuit. During the measurements, the regulation requires a certain stabilization time before taking reliable test values. In other words, a certain waiting time is required before making the measurements that determine the coil connections' electric resistance and the coils' electric resistance. The waiting time is typically due to the filtering effect of the feedback regulation system. The waiting time is a penalizing time, which decreases the number of cores that can be tested in a certain time by a testing machine.
In addition to the above, a same testing machine is often used both for measuring the coil connections' resistance, and the coils' electric resistance of cores, where the coils have significantly different sizes. These coils of different core categories can have very different inductive and electric resistance ranges. Consequently, and particularly in the situation of coils having large electric resistance values, the small current that is applied for carrying out the measurement can easily be partially dispersed. This results in less precision in the determination of the coil connection electric resistance and the coil electric resistance.